linux-kernel - Re: [PATCH v2 3/4] PM: domains: Drop/restore performance state votes for devices at runtime PM

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Date:   Thu, 3 Jun 2021 22:08:43 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        linux-pm@...r.kernel.org
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Stephan Gerhold <stephan@...hold.net>,
        Roja Rani Yarubandi <rojay@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/4] PM: domains: Drop/restore performance state votes
 for devices at runtime PM

03.06.2021 22:02, Dmitry Osipenko пишет:
> 03.06.2021 12:34, Ulf Hansson пишет:
>> A subsystem/driver that need to manage OPPs for its device, should
>> typically drop its vote for the OPP when the device becomes runtime
>> suspended. In this way, the corresponding aggregation of the performance
>> state votes that is managed in genpd for the attached PM domain, may find
>> that the aggregated vote can be decreased. Hence, it may allow genpd to set
>> the lower performance state for the PM domain, thus avoiding to waste
>> energy.
>>
>> To accomplish this, typically a subsystem/driver would need to call
>> dev_pm_opp_set_rate|opp() for its device from its ->runtime_suspend()
>> callback, to drop the vote for the OPP. Accordingly, it needs another call
>> to dev_pm_opp_set_rate|opp() to restore the vote for the OPP from its
>> ->runtime_resume() callback.
>>
>> To avoid boilerplate code in subsystems/driver to deal with these things,
>> let's instead manage this internally in genpd.
>>
>> Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
>> ---
>>
>> Changes in v2:
>> 	- Rebased.
>> 	- A few minor cosmetic changes.
>> 	- Deal with the error path in genpd_runtime_resume().
> 
> I tested this on NVIDIA Tegra by removing the boilerplate code from
> drivers' RPM and haven't noticed any problems, the performance state is
> dropped/restored as expected. Thank you.
> 

Tested-by: Dmitry Osipenko <digetx@...il.com>